Caracterização morfológica e padrões de crescimento durante o desenvolvimen-to inicial de Brycon Falcatus (Characiformes: Bryconidae) da Sub-Bacia do Rio Ta-pajós.

Abstract

Brycon falcatus Müller & Troschel, 1844, belonging to the family Bryconidae and the order Characiformes, is a species of great relevance in the Tapajós River sub-basin, standing out both for its importance for fishing and for its ecological role as a seed disperser. However, little is known about its early development, due to the scarcity of information that allows its precise identification. Thus, this study aims to describe the larval and juvenile stages of B. falcatus, using morphological, meristic and morphometric data, in addition to analyzing the growth patterns during the larval phase. The biological material used was collected between 2016 and 2024, in the Tapajós River sub-basin, in the Teles Pires and Tapajós River water systems. A total of 116 individuals were analyzed, four in the yolk larval stage, 27 in pre-flexion, 61 in flexion, 16 in post-flexion and eight in the juvenile period. The standard length ranged from 4.02 mm (yolk larval) to 72.83 mm (juvenile). Using the morphometric data, analytical regression models were tested to evaluate growth. The larvae have a robust and elongated body, with a terminal, slightly prognathic and oblique mouth, with teeth. The intersection of the maxilla and mandible surpasses the eye, and the intestine is long, extending beyond half of the body. Pigmentation in the larval stage is composed of dendritic and punctiform chromatophores, forming a dark spot that covers the entire body surface, including the embryonic membrane. Juveniles have dark longitudinal stripes, a macula after the head and a spot on the peduncle that extends to the lobes of the caudal fin. The number of myomeres varies from 42 to 44, and the sequence of fin ray formation is: caudal (9-10 main), dorsal (i+10), anal (i+24-25), pelvic (i+7) and pectoral (i+13). Most biometric measurements indicate proportional increase, and growth reveals different changes in the development of this species. B. falcatus larvae can be distinguished from congeners by the number of myomeres and the pigmentation pattern. In juveniles, differentiation occurs by pigmentation and the number of fin rays. This information is essential for the correct identification of larvae captured in the wild, aiding in the location of drift and nursery areas used by the species, and directing effective management and conservation actions and measures.